1. Field of the Invention
The present invention relates to a sensing device for sensing when a car seat is occupied.
2. Description of the Related Art
FIG. 10 shows a car seat 1, to which a seat-occupant sensing device 4 is mounted to the seat cushion 3, to which a seat back 2 is mounted via a seat-reclining mechanism. The seat-occupant sensing device 4 is provided at approximately the center (as shown by the diagonal lines) of the seat cushion 3, where an occupant will sit
FIG. 11 shows a wide mat-type conventional seat-occupant sensing device 4. The seat-occupant sensing device 4 consists of a flat sensor-support part 5, a plurality of pressure sensors 6 that are affixed to the sensor-support part 5, a wire 7 that connects said pressure sensors 6 with a harness wire 8 that is designed to conduct sensing signals.
FIG. 12 is a cross-section from-front-to-back view of a seat cushion 3 along the line A of FIG. 10. Cushion springs 10 are installed in the cushion frame 9, on which is installed a cushion pad 11 that is composed of foam urethane. A seat-occupant sensing device 4 is installed on the cushion pad 11, which is covered with a trim cover 12. With such a structure, because the seat-occupant sensing device 4 senses a load when a passenger or a driver is seated on a seat 1, it is possible to know whether a seat is occupied or not.
However, a conventional seat-occupant sensing device 4 has the following problems.
(1) When a mat-like heater is built into the seat cushion 3, the heater is laminated on the mat-type seat-occupant sensing device 4. However, when such a heater is placed on the sensing device, two layers of lamination are formed, resulting in a hard and uncomfortable seat surface.
(2) Because the performance characteristics of a mat-type seat-occupant sensing device 4 tend to vary depending on the temperature, the performance of the sensors tends to be adversely affected by the heat that they are subjected to when the seat-occupant sensing device 4 is covered by such a heater.
(3) When the trim cover 12 is broken or damaged, the seating sensor 4 beneath the cover might also be damaged and its performance adversely affected.
(4) When the cushion pad 11 and the trim cover 12 become worn as time elapses, the sensing capabilities of the seat-occupant sensing device 4 deteriorate.
In view of the conventional problems, the objective of the present invention is to provide a car-seat-occupant sensing device wherein (1) a mat-like heater can be installed in a seat, such as in the seat cushion, without adversely affecting a seat""s sitting comfort for a driver or passenger, and (2) damage to the sensing device can be prevented.
For the purpose of achieving the above-mentioned objective, the seat-occupant sensing device of the present invention is characterized such that (1) the area between two electrodes that face each other is increases or decreases due to the contraction or extension (lengthening), respectively, of a pressure-detecting spring, (2) the sensing device is equipped with (a) load sensors that conduct electrostatic capacitance, which changes in accordance with the increase or decrease of the area between the aforementioned electrodes, and (b) cushion springs that are installed in the seat frame, and (3) one end of each of said pressure-detecting spring is connected to the seat frame and the other end is connected to the end of a cushion spring.
The load sensor is constituted such that two electrodes that face each other constitute a capacitor. Thus, when a person sits on a car seat, a load is placed on a sensor, causing the pressure-detecting springs to extend (lengthen). As a result, the area between the two electrodes that are related to each pressure-detecting spring becomes smaller, whereby the sensor determines that a load is being applied thereon.
According to the present invention, when a person sits on a seat the cushion springs are caused to flex as a result of the load that is applied by the person sitting on the seat. Because this flexing is transmitted to the load sensors, seating can be sensed. Therefore, the load sensor does not have to be formed into a wide mat-shape, nor to be placed at the portion of the seat where a person""s buttocks rest when the person is sitting in the seat. Thus, the cushioning property of the seating portion of the seat is not adversely affected, and sitting comfort can be maintained. Also, if the cushion pad and the trim cover are broken, the load sensor is not broken, nor is its performance adversely affected. Furthermore, if a mat-like heater is installed in the seat, the heat that is emitted from the heater is not conveyed to the load sensors.
The seat-occupant sensing device for a car seat of the invention is characterized such that (1) the area between two electrodes that face each other increases or decreases due to the contraction or lengthening, respectively, of the aforementioned pressure-detecting spring, (2) the sensing device is equipped with (a) a load sensor that conducts electrostatic capacitance, which changes as the area between the electrodes increases or decreases, and (b) a sensing plate that is installed in the seat frame via a fixing spring, and (3) one end of each of said pressure-detecting springs is connected to the seat frame and the other end is connected to the sensing plate.
According to the present invention, because the sensing plate senses the load of a person sitting on the seat and the spring is then flexed (lengthened), the load sensor that is connected with the spring can sense when a person sits on the seat. In this invention, because a load sensor does not have to be installed in the seating portion of the seat, a seat heater can be installed in the seat while sitting comfort can be maintained, and the load sensor is not adversely affected if the cushion pad or trim cover is broken, as mentioned above.
The invention is further characterized such that (1) said load sensor is equipped with a pair of insulated inner and outer tubular members, each of which is attached to one end of a detecting-spring, (2) two electrodes face each other, with one being on the outside of the inner tubular detecting-spring holding member (hereinafter xe2x80x9cinner holding memberxe2x80x9d) and the other being on the inside of the outer tubular detecting-spring holding member (hereinafter xe2x80x9couter holding memberxe2x80x9d), (3) both the inner and outer holding members move in opposite directions as the pressure-detecting spring extends or contracts, and (4) the outer holding member slides rectilinearly along a movement-guiding member that is a part of the inner holding member.
In this invention, because both the inner and outer holding members move, thereby causing an increase or decrease in the area between the aforementioned two electrodes that face each other, a load can be detected. And because each pair of the holding members slide rectilinearly in opposite directions, variations of the electrostatic capacitance between the holding members can be sensed with great accuracy.
The invention is further characterized such that the aforementioned load sensor is equipped with (a) a pair of insulated inner and outer holding members, which can move in opposite directions as the aforementioned pressure-detecting spring extends or contracts, and each of which is attached to one of the aforementioned two electrodes, as described above, and (b) an insulating spacer that is placed between the inner and outer holding members.
In this invention, because both the inner and outer holding members move, thereby causing an increase or decrease in the area between the aforementioned two electrodes that face each other, a load can be detected. Also, because the aforementioned insulating spacer acts to maintain a constant gap between the aforementioned two electrodes, when the aforementioned holding members move the electrostatic capacitance between the electrodes varies rectilinearly when a load is detected but returns to the constant-gap value after the load is removed (i.e., after the person gets out of the seat), which ensures that the sensor is able to accurately measure variations in the load as different persons sit in or leave the seat. Thus, the sensing device can detect not only when a person sits in the seat, but it can also easily measure the weight of that person and can detect when the person gets out of the seat.